1. Field of the Invention
The present invention relates to a magnetic recording method and a magnetic reproducing method and, more particularly, to a magnetic recording method for effecting high-density magnetic recording of a digital signal as well as to a magnetic reproducing method for reproducing a digital signal which has been magnetically recorded with high density.
2. Description of the Related Art
One known example of an apparatus for carrying out such methods is a digital video tape recorder (VTR) for recording and reproducing a digital video signal.
Typical digital VTRs are required to effect high-density digital recording so that a large amount of data can be handled. To achieve the high-density digital recording, it is an essential requirement to increase the S/N ratio of the magnetic recording system of such a digital VTR.
A tape-shaped magnetic recording medium (hereinafter referred to as the "metal evaporated tape") in which a magnetic layer is formed on a base film by a vapor deposition process, is known as one type of high-density magnetic recording medium. Such a metal evaporated tape is generally superior in its magnetic characteristics, such as residual magnetic flux density, to a metal particle tape and can provide a high-level reproduction output, particularly in a short-wavelength range. For the above and other reasons, the metal evaporated tape promises highly as a medium for high-density magnetic recording, and a medium consisting essentially of Co-Ni has presently been put into practice.
Heretofore, a partial response (1, 0, -1) method is generally employed for digital recording on a metal evaporated tape. This is because a waveform response obtained by recording or reproduction on or from a metal evaporated tape shows a large nonlinear distortion in its low-frequency range compared to that obtained by recording or reproduction on or from a metal particle tape, as will be described later.
In contrast to other methods such as an integration detection method, the partial response (1, 0, -1) method does not need low-frequency compensation and is capable of reducing the influence of the aforesaid low-frequency distortion of the metal evaporated tape. The partial response (1, 0, -1) method is disclosed in "Nakagawa et al, Comparative Examination of Detection Methods in NRZ Recording, Shingakugihou, MR78-3 (Aug., 1978)". Since the partial response (1, 0, -1) method is not directly related to the present invention, a detailed description of the technical contents is omitted.
The partial response (1, 0, -1) method referenced in the above explanation of the conventional example, however, has a number of disadvantages. For example, the timing margin at a signal detection point is small, and since detection of three levels is performed, the optimum value of the threshold level of a comparator at the signal detection point varies due to level variations in reproduction output.
As a result, if high-speed, high-density recording and reproduction are to be realized by utilizing the feature of the metal evaporated tape, i.e., a high S/N ratio, the above-described characteristics of the partial response (1, 0, -1) method will be a great disadvantage, since they increase the instability (jitter, dropout, etc.) of the magnetic recording system to a remarkable extent.
As a technique for reducing the influence of the low-frequency distortion of a metal evaporated tape, it is also considered to use a modulation method, such as M.sup.2, 8-14 conversion, to suppress greatly the low-frequency component of a recording signal. However, this method is still undesirable, in that the amount of data to be processed increases greatly and the interval of detection windows is made small.